In the chronic experimental hydrocephalic cat, the dilated spinal cord central canal provides the major alternate pathway for the egress of cerebrospinal fluid from the cerebral ventricles. Despite the apparent arrest of the hydrocephalic process, in these animals, the removal of the calvarium and underlying dura results in massive ventriculomegaly. Therefore, the degree to which the dilated central canal is an effective pathway will be determined by measuring the compliance and outflow resistance of spinal fluid from this canal both before and after craniectomy. When the flow of spinal fluid through the central canal is obstructed, the intraventricular pressure rises and intracranial pressure plateau waves develop. Cerebrospinal fluid formation, cerebral blood flow, systemic blood pressure, and the effects of drugs on the appearance and disappearance of these waves will be studied. Choroid plexus function (spinal fluid secretion, glucose and sodium transfer from blood) will be evaluated in these experimental hydrocephalic cats to determine the effects of the hydrocephalic process on this organ. Choroid plexus blood flow in both normal and hydrocephalic cats will be measured and compared to determine whether the noted decrease in cerebrospinal fluid formation in hydrocephalic cats can be attributed to a decrease in blood flow through this organ. Cerebrospinal fluid volume flow, sodium and glucose influx rates will be measured during cerebral ventricular perfusion with anisotonic sucrose solutions. The perfusion technique will also be used to evaluate the role of the choroid plexus, and blood-brain barrier on glucose exchange between blood and spinal fluid.